Fork lift trucks



March 20, 1962 E. MEISTER FORK LIFT TRUCKS 2 Sheets-Sheet 1 Filed June 24, 1960 INVENTOR.

FORK LIFT TRUCKS Filed June 24, 1960 2 Sheets-Sheet 2 Li. 9 7 g 6 INVENTOR I? 22?? rxy n Wane/e- United States Patent 3,026,089 FORK LIFT TRUCKS Erwin Meister, Deisberg, Switzerland, assignor to Gesellschaft der Ludw. von Rollschen Eisenwerke A.G., Gerlafingen, Switzerland, a company of Switzerland Filed June 24, 1960, Ser. No. 38,553 Claims priority, application Switzerland June 30, 1959 Claims. (Cl. 254-2) This invention relates to fork lift trucks and more particularly to hand-operated pallet lift trucks having a load carrier which is adjustable as to height by operating the drawbar.

It is a first object of the invention to provide a fork lift truck which has an increased load-carrying capacity.

A further object is to provide a fork lift truck with an improved parallel displacement of the forks.

A further object of the invention is to provide a fork lift truck whereby the force required for the first few pump strokes is smaller than for the last pump strokes.

These and other objects of the invention will become further apparent from the following detailed description, reference being made to the accompanying drawings, showing a preferred embodiment of the invention.

FIG. 1 is a perspective view of a lift truck with the fork in the raised position,

FIG. 2 is a detail of the front part on the lowermost position of the fork, and

FIG. 3 is a detail view of the rear part of the lift truck in its lowered bottom position,

FIG. 4 is a front view of the front portion of the lift truck.

The hand-operated lift truck shown has a carrier to receive the load to be transported and includes two vertically movable members 1 forming a fork rigidly joined to a vertical member 2, which in turn carries a projecting angular support plate 3. A piston rod 4 is movable up and down in the axial direction of a pressure cylinder 5 and bears freely against the plate 3. The bottom of the pressure cylinder 5 lies against a yoke 6 which is rotatably supported and carries two steerable front wheels 8. On each side of the yoke a front arm 9 is pivoted about a bolt or a spindle or axle 18. Since both sides of the lift truck are of symmetrical construction, hereinafter only one side will be described. The other end of the arm 9 is pivoted to the front end of the load bearing fork 1 by means of a bolt or a spindle or axle 10.

A connector pin 11 is disposed somewhat behind and above this ale to which a pull-rod 12 is pivotally linked. Said pull-rod 12 extends rearwardly inside the fork, which is of U-shaped cross-section, and carries a connector pin 16 rotatably in a rear arm 15. Said arm is pivotally mounted about a pivot 17 in the fork 1 and carries, at its end, a wheel 19 which rests on the ground.

A connecting line through the axis of the pivot 17 and the pin 16 forms an angle [3 of approximately 90 to the fork surface 1 when the fork is in its lowermost position. As the height of the fork 1 increases, the said angle 5 (which lies between 85 and 95) decreases, as will be clear from the chain-dotted position of the fork shown in the upper section of FIG. 3.

In the lowermost, i.e., depressed position of the fork 1 the angle a between the upper fork surface 1' and a line connecting the center of the axle 10 holding the arm 9 on the load-carrier and the center of the pin 11 on which the pull-rod is fastened, is less than 150, preferably between 130 and 140, for example, about 135.

In the case of the front arm 9, a line connecting the axis of the spindle 18 and the axle 10 encloses an acute angle 6 with the ground when the forks are in the lowermost position (FIG. 2). The top position of the fork 1 and of the arm 9 is shown in chain-dotted lines in FIG. 2.

The lever arm a is formed by the distance between the axle 18 and the axle 10; the lever arm b corresponds to the distance between the axle 10 and the pivot pin 11. The ratio of the shorter lever arm 15 to the longer lever arm a is at least 123.8, and is preferably between 1:4 and 1:5 and preferably about 124.3.

In a preferred practical embodiment the angle 6 is 22, the lever arm a120 mm., the lever arm b=28 mm. (a ratio of 1+4.3) and the difierence between the highest and lowest fork positions 110 mm. In the case of the rear arm 15, the distance from the axis of pivot pin 17 to the axis of the wheel 19:150 mm., the diameter of the rear wheel 19:90 mm., the diameter of the front wheels 8:200 mm., and the distance of the pivot pin 17 from the pull-rod pivot pin 16 is 28 mm. with an angle [3 of thus giving the most favorable position for the application of the pull of the pull-rod 12 and, accordingly, the minimum force is required for the movement of the arm 15. In this embodiment, the axles 10 and the axis of the piston rod 4 lie in a vertical plane.

The mode of operation is as follows: the forks 1 of the pallet lift truck are slid beneath the article to be transported, for example, a case resting on support blocks or feet. The draw-bar is then moved up and down in the direction of the arrow 20 to operate piston of the hydraulic pump 7, which, by means of this small piston, forces oil into the greater pressure cylinder 5, so that the piston situated therein, together with the piston rod 4, moves in the upward direction and thus lifts the supporting plate 3 together with the vertical member 2 and the forks 1. As a result, the arms 9 are swung about the pivots 18, which pivots are fixed in respect of their vertical position. Since the axles 10 do not vary their position relatively to the load-carrier or the forks, the movement is transmitted by the arm 9, which acts as a two-armed lever, to the pin 11 and thence to the pullrod 12, by which a pull is exerted on the arm 15, so that the angle to the ground is reduced, with the result that the form 1 rises parallel to the ground. Depending on the height to which the article to be transported is to be raised above the ground, a larger or smaller number of pump strokes with the drawbar 13 will be necessary. After the article to be transported has been raised sufficiently, the hand-operated lift truck together with the said article is pulled by hand or by a powered tractor to the required place, whereupon the oil is let out of the pressure cylinder 5 by a release valve, Operated by a lever 21, so that the piston rod 4, and hence the forks 1 are lowered clear of the load. The lift truck can then be drawn away empty.

In the special construction of the lever arms described, the angle of application of the force, and the proportions chosen, enable the displacing forces, especially the traction on the pull-rod 12, to be made relatively small for a given lift and a given load, and yet a very substantial parallel vertical displacement of the fork will be obtained in the end position as well as in the intermediate positions. A further effect achieved is that the force required for the first few pump strokes, is smaller than for the last pump strokes, in comparison with hitherto known hand-operated lift trucks, and this is also very desirable, since only in very few cases is the full lift height used for the transportation of goods and hence greater ease of operation is obtained for the cases occurring most frequently in practice.

With otherwise identical mechanical conditions the maximum load-carrying capacity of the lift trucks can be greatly increased, since, apart from adequate mechanical strength, the said load-carrying capacity is dependent primarily on the pumping force that has to be applied to the draw-bar.

Various changes and modifications may be made without departing from the spirit and scope of the present invention, and it is intended that such obvious changes and modifications be embraced by the appended claims.

What I claim is:

1. A hand operated lift truck comprising vertically movable load carrier means, a substantially vertical member rigidly joined to the load carrier means, supporting means fixed to the upper end of the vertical member and extending substantially in horizontal direction, at least one axle supported steerable front wheel arranged in front of said load carrier means and beneath said supporting means, a cylinder and a movable piston therein arranged vertically between said front wheel and said supporting means, a yoke pivotally engaging said pressure cylinder, said piston projecting out the top of said cylinder and bearing against said supporting means, said front wheel being attached to the lower end of said cylinder, front arms pivotally connected to said yoke and to said load carrier means on both sides of the front wheel, rear wheels beneath said load carrier means, rear arms pivotally carrying the rear wheels and pivotally connected to the load carrier means, pull rod means extending between and connected to the front and rear arms, the angle between the upper surface of the load carrier means and a line connecting the axis on which said front arm is supported on said load carrier means and the axis on which the pull rod is fastened to the front arm being less than 150 in the lowermost position of the load carriermeans, the angle formed between said upper surface of the load carrier means and a line connecting the axis on which the rear arms are pivoted on said load carn'er means and the axis on which the pull rod is connected to said rear arms being substantially equal to 90 to thereby obtain a best possible parallel displacement of the load carrier means during lifting.

2. A hand operated lift truck comprising a vertically movable fork carrying the load, a substantially vertical member rigidly joined to the fork at the front end, a supporting plate fixed to the upper end of the vertical member and extending forwardly therefrom substantially parallel to the fork, at least two steerable front wheels arranged in front of said fork and beneath said supporting plate, a vertical pressure cylinder and a movable piston therein extending out the upper end thereof, a yoke pivotally engaging said pressure cylinder at the lower end thereof, said piston bearing against the under side of said supporting plate, said front wheels being carried by the lower end of said cylinder, front arms pivotally connected to said yoke and to said load carrier means on both sides of the front wheels, rear wheels beneath the fork at the rear thereof, rear arms pivotally carrying the rear wheels and pivotally connected to the fork, pull rod means extending between and pivotally connected to the front and rear arms, the angle between the upper surface of the fork and a line connecting the axis. on which said front arm is pivoted on said load carrier means and the axis on which the pull rod is connected to the front arm being between 130 and 140 in the lowermost position of the load carrier means, the angle formed between said upper surface of the load carrier means anda line connecting the axis on which the rear arms are connected to said load carrier means and the axis on which the pull rod is connected to the rear arms being between and and the ratio between inter-pivot lengths of the front arms being between 1:4 and 1:5 to thereby obtain the best possible parallel displacement of the load carrier means during lifting.

3. A hand operated lift truck according to claim 1, wherein the axis on which the front arms are connected to the yoke lies substantially in the same vertical plane as the axis of the pivotal connection between the yoke and cylinder.

4. A hand operated lift truck according to claim 2, wherein in the fully lowered position the angle between the ground and the line connecting the axis on which the front arm is connected to the yoke and the center of the axis on which said arm is supported on the fork is between 15 and 30.

5. A hand operated lift truck comprising a vertically movable fork carrying the load, a substantially vertical member rigidly joined to the fork at the front end, a supporting plate fixed to the upper end of the vertical member and extending forwardly therefrom substantially parallel to the fork, at least two steerable front wheels arranged in front of said fork and beneath said supporting plate, a vertical pressure cylinder and a movable piston therein extending out the upper end thereof, a yoke pivotally engaging said pressure cylinder at the lower end thereof, said piston bearing against the under side of said supporting plate, said front wheels being carried by the lower end of said cylinder, front arms pivotally connected to said yoke and to said load carrier means on both sides of the front wheels, rear Wheels beneath the fork at the rear thereof, rear arms pivotally carrying the rear wheels and pivotally connected to the fork, pull rod means extending between and pivotally connected to the front and rear arms, the angle between the upper surface of the fork and a line connecting the axis on which said front arm is pivoted on said load carrier means and the axis on which the pull rod is connected to the front arm being approximately in the lowermost position of the load carrier means, the angle formed between said upper surface of the load carrier means and a line connecting the axis on which the rear arms are connected to said load carrier means and the axis on which the pull rod connected to the rear arms being approximately 90, the ratio between the inter-pivot length of the front arms being 120:28, and the ratio between the inter-pivot length of the rear arms being :28 thereby to obtain the best possible parallel displacement of the load carrier means during vertical movement thereof.

References Cited in the. fileof this patent UNITED STATES PATENTS 2,424,417 Quayle July 22, 1947 2,681,202 Germond June 15, 1954 FOREIGN PATENTS 1,172,380 France Oct. 13, 1958 

